Did the above and tested again - still the same but I tried the other ear which I have set for "Next Track" and that too turns the radio off and starts Apple Music.
One other test - left it on Siri and Siri did come up and not Apple Music.
Next: made sure Apple music was closed but it still started playing music with a double tap.
Next: turned off the double tap and that works because it didn't do anything
Next: started Apple Music and double tap works fine.
Next I will try another app - Tried NGEN Radio and it works fine. It might just be the Sports Day app.
Apps that work - Amazon Music, Way-FM and NGEN Radio
I am leaning towards the Sports Day app not working properly.
Yep. Possibly an app issue. I don't use mine but for phone calls and Apple Music.